Valves used for intercepting the most varied fluids have long been available commercially. Such valves are much used particularly in the coffee machine sector, especially for machines of professional type. Electromagnetically operated valves are frequently used in this sector.
Professional coffee machines present a boiler connected to a dispensing unit via suitable fluid passages interceptable by said solenoid valves. The dispensing unit comprises in one surface a pair of holes of standardized diameter and distance between axes. The first hole communicates with the spray head of the coffee machine, while the second hole is fed with pressurized hot water from a suitable boiler.
A valve of conventional type is mounted on the surface of the dispensing unit. This valve comprises a valve body in which, in a surface thereof connected to the dispensing unit, two holes are provided having their diameter and distance between axes identical to those provided in the dispensing unit; one of the two is provided in a position axial to the valve, while the second is provided in a side position. At the connection surface the valve body supports a pair of gaskets positioned about the two holes provided in the valve body. The valve body supports an axially holed bush, usually of stainless steel. In that side of the valve body opposite the connection surface there is provided an internally threaded dead-ended hole coaxial with the valve body. This hole communicates with the axial hole via the bush, and with the side hole. An externally threaded ring welded to a core guide tube is screwed into the thread.
The cup-shaped piece is closed at its top by an element welded to it. This element can be of different form depending on the type of valve to which it is welded. In particular it can differentiate a three-way valve from a two-way valve. A conventional valving element (or moving core) is movable in the core guide tube between a first and a second position against a spring. When in its first position the valving element abuts against the steel bush and closes its hole. When in its second position it frees the bush hole and connects it to the side hole of the valve body, to allow fluid passage. Consequently, when the valving element is in its first position the dispensing unit is not fed, whereas when the valving element is in its second position the pressurized hot water flows from the axial hole to the side hole, through the first hole of the dispensing unit towards the spray head.
A valve conceived in this manner presents considerable drawbacks. A first of these is that it is constructionally complicated. In this respect, to construct it the valve body has to be cast and then mechanically machined. The mechanical machining operations to be carried out on this component are extremely complex as it has to be drilled in several points, it has to be milled, the seat for the bush has to be formed and threaded. This all starts from a workpiece usually of forged brass construction. The choice of brass lies in its simplicity of machining by chip removal and for its resistance to utilization temperatures. In addition a ring has to be made and welded to the cup-shaped piece.
A further drawback of the known art is that to make the brass compatible with food use (to avoid extraction of the zinc or lead contained in the alloy), it is covered with a nickel layer, usually by a chemical bath (Nipploy process or Nichel Chimico). This nickel plating gives rise to a series of problems. Firstly, it represents a further operation to which the valve body has to be subjected. Even if this operation is carried out with care, it is always possible for nickel residues to remain, which contaminate the water passing through the valve body. Finally, if the nickel plating is not perfect and if chlorine is contained in the water (as is often the case in water originating from the domestic main), the chlorine attacks the nickel and penetrates below it, between the nickel layer and the brass, to gradually detach the entire coating. Hence although nickel plating eliminates the problem of water contamination by the lead or zinc contained in the brass, it creates the possible problem of water contamination by nickel.